The present invention relates to a process for the synthesis of unsaturated aldehydes. More specifically, it relates to a process for the synthesis of unsaturated aldehydes from allylic tertiary amines
It is known in the prior art to prepare tertiary amine N-oxides by oxidation of the corresponding amines in the presence of a hydroperoxide and a metal catalyst. In particular, Sheng et al. (J. Org. Chem. 33:588 (1968); Organic Synthesis 50:56 (1970)) describe the preparation of tri-n-butylamine, triethylamine and 1-dimethylamino-2-propanol N-oxides. In paticular, the metals used are vanadium, molybdenum, chromium, cobalt, iron and manganese; the hydroperoxide being chosen from cumyl and amylene hydroperoxides.
It is also known to carry out the N-dealkylation of tertiary amines in the presence of a ruthenium catalyst and tert-butyl hydroperoxide (Murahashi et al., Am. Chem. Soc. 110:8256 (1988)). This process is especially well-suited to the selective demethylation of tertiary methylamines.
However, none of these documents describes or suggests the possibility of oxidizing tertiary amines directly to aldehydes. Moreover, nothing in these documents suggests the possibility of directly oxidizing allylic tertiary amines, the reactivity of which is different from that of the aliphatic amines described in the prior art.
Applicants have now shown that it is possible to oxidize allylic tertiary amines to form the corresponding unsaturated aldehydes. Moreover, Applicants likewise show that the oxidation also leads to the formation of the corresponding enamine.